Different human vaccine adjuvants promote distinct antigen-independent immunological signatures tailored to different pathogens

Guided design for the development of an evolution-proof influenza vaccine

Influenza remains a significant public health concern, particularly among high-risk populations, due to its capacity to cause annual epidemics and potentially trigger global pandemics. Despite the availability of countermeasures such as vaccines and antiviral treatments, their effectiveness is hindered by factors such as resistance development with manufacturing of the influenza vaccine still heavily relying on decades-old technologies. This review therefore examines the mechanisms by which influenza viruses evade host immunity and evaluates current and emerging approaches to enhance vaccine-mediated protection. Advances targeting the conserved hemagglutinin (HA) stem, incorporating multiple HA subtypes, and the use of adjuvants are discussed, alongside increased attention to neuraminidase (NA) and other viral components as immunogenic targets. Strategic epitope prediction, through glycan masking, evolutionary forecasting, and consensus sequence design, offer promising frameworks for rational vaccine design. Furthermore, delivery platforms, including recombinant protein, mRNA, and conjugate vaccines are explored for their potential to elicit broad and durable immunity. Collectively, these developments highlight a multifaceted approach towards the design of effective interventions against this persistent healthcare challenge.

Role of NLRP3 inflammasome in nanoparticle adjuvant-mediated immune response

The nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome is pivotal in orchestrating the immune response induced by nanoparticle adjuvants. Understanding the intricate mechanisms underlying the activation of NLRP3 inflammasome by these adjuvants is crucial for deciphering their immunomodulatory properties. This review explores the involvement of the NLRP3 inflammasome in mediating immune responses triggered by nanoparticle adjuvants. It delves into the signaling pathways and cellular mechanisms involved in NLRP3 activation, highlighting its significance in modulating the efficacy and safety of nanoparticle-based adjuvants. A comprehensive grasp of the interplay between NLRP3 inflammasome and nanoparticle adjuvants holds promise for optimizing vaccine design and advancing immunotherapeutic strategies.

Characterizing TLR4 agonist EmT4™ as an anti-Mycobacterium tuberculosis vaccine adjuvant

Tuberculosis (TB) is again the deadliest infectious disease globally, and more efficacious vaccines are needed to reduce this mortality. Successful subunit TB vaccines need antigens and adjuvants that are immunogenic, inexpensive, and accessible. Here we evaluated the potential of synthetically produced Monophosphoryl lipid A (SyMLP), a TLR4-agonist, formulated in an oil-in-water emulsion (EmT4™) in combination with selected fusion proteins, to drive an effective vaccine-mediated immunogenic response in C57BL/6 mice against Mycobacterium tuberculosis (M.tb) HN878 and H37Rv challenge. We first observed that EmT4™ enhances activation of C57BL/6 bone-marrow derived macrophages and dendritic cells measured by CD40, CD86, and MHCII expression by flow cytometry. EmT4™ did not induce safety signals in a scaled tolerability study. In immunogenicity studies, mice immunized 3 times 3 weeks apart with ID93 antigen + EmT4™ produced a significantly higher magnitude of circulating proinflammatory cytokines and ID93-specific immunoglobulin G (IgG) antibodies pre- and post-challenge with M.tb than saline control animals. Ex vivo ID93 restimulated splenocytes and lung cells elicited significant polyfunctional CD4+ T-helper 1 responses. Importantly, ID93 + EmT4™ immunizations significantly reduced bacterial burden in C57BL/6 mice 4 weeks post-challenge. Interestingly, EmT4™ paired with a next generation protein fusion ID91 also afforded prophylactic protection against M.tb HN878 challenge in both young (6 to 8 wk) and aged (20 mo) immunocompromised Beige mice. These protection and immunogenicity findings suggest that synthetically derived EmT4™ adjuvant is not only suitable to help backfill the preclinical TB vaccine candidate pipeline but is also suitable for the needs of the global community.

Novel tuberculosis vaccines based on TB10.4 and Ag85B: State-of-art and advocacy for good practices

Tuberculosis (TB) has plagued humanity in numerous devastating forms for centuries and remains a significant health challenge. Mycobacterium tuberculosis (Mtb), the bacterium responsible for TB, was the leading cause of death among infectious agents until the COVID-19 pandemic emerged. Immunization with the bacillus Calmette-Guérin (BCG) vaccine is one of the primary strategies to mitigate the risk of TB. Despite its widespread use, the current BCG vaccine has limited efficacy, particularly in adults. This review focuses on the rational design of vaccine candidates targeting the antigens TB10.4 and Ag85B. The review discusses the roles of TB10.4 and Ag85B in the virulence of Mtb and notes challenges in their production. Additionally, various protein conjugation strategies to enhance immunogenicity, including linking these antigens to glycans and adjuvants, are considered, as well as the most appropriate analytical methods for characterizing recombinant antigenic proteins and their conjugates. Finally, the associated challenges in developing a vaccine encompassing specific glycans and protein components were highlighted. We claim that using standardized procedures and detailed reporting in protein production and chemical modification can improve the reproducibility and rationalization of biological results. By adhering to these guidelines, the goal of developing an effective vaccine against TB will be best achieved.

Post-exposure vaccine protection of CTH522/CAF®01 against reinfection with Chlamydia trachomatis requires Th1/Th17 but not Th2-immunity

Chlamydia trachomatis (C.t.) is globally the most common sexually transmitted bacterium with an estimated 131 million new cases occurring every year. There is no licenced vaccine against C.t. Repeated infections are often observed in women, suggesting that natural immunity is only partially protective. It is therefore important to investigate if a vaccine given post exposure, on top of a partially protective natural immunity, can increase protection against reinfection. In mice, an infection leads to robust immunity to subsequent challenges that precludes an investigation of increased protection elicited by a post-exposure vaccine. Therefore, we developed a new animal model where the first infection only provided partial protection against reinfection. Using this model, we show that UV-SvD/CAF®01 and CTH522/CAF®01 as post-exposure parenteral vaccines, but not CTH522/AlOH, protected against reinfection. As CTH522/CAF®01 also reduced the gross pathology score post reinfection, this suggests that CTH522/CAF®01 is both protective and safe as a post-exposure vaccine.

Subunit antigen delivery: emulsion and liposomal adjuvants for next-generation vaccines

INTRODUCTION

Developing new vaccines to combat emerging infectious diseases has gained more significance after the COVID-19 pandemic. Vaccination is the most cost-effective method for preventing infectious diseases, and subunit antigens are a safer alternative to traditional live, attenuated, and inactivated vaccines.

AREAS COVERED

Challenges in delivering subunit antigens and the status of different vaccine adjuvants. Recent research developments involving emulsion and liposomal adjuvants and their compositions and properties affecting their adjuvancy.

EXPERT OPINION

Lipid-based adjuvants, e.g. emulsions and liposomes, represent a paradigm shift in vaccine technology by enabling robust humoral and cellular immune responses with lower antigen doses, a property that is particularly critical during pandemics or in resource-limited settings. These adjuvants can optimize vaccine administration strategies by potentially reducing the frequency of booster doses, thereby improving patient compliance and lowering healthcare costs. While emulsions excel in dose-sparing and broadening immune responses, liposomes offer customization and precision in antigen delivery. However, the broader clinical application of these technologies is not without challenges. Stability issues, e.g. the susceptibility of emulsion-based adjuvants to freezing and their reliance on cold-chain logistics, pose significant barriers to their use in remote/underserved regions. Future developments will likely focus on improving manufacturing scalability and cost-effectiveness.

Inflammatory and Humoral Immune Responses to Commercial Autogenous Salmonella Bacterin Vaccines in Light-Brown Leghorn Pullets: Primary and Secondary Vaccine Responses

BACKGROUND/OBJECTIVES

Commercial poultry flocks undergo Salmonella vaccinations to manage salmonellosis outbreaks. Due to reports of severe injection site reactions to Salmonella bacterins, assessment of local inflammatory responses is necessary. The objective was to assess local inflammatory and systemic humoral immune responses to commercial autogenous Salmonella bacterin vaccines (SV1 or SV2) following primary or secondary intradermal (i.d.) vaccination in Light-Brown Leghorns (LBLs).

METHODS

LBL pullets received primary (14 wks) or secondary (19 wks) vaccination by i.d. growing feather (GF) pulp injection of SV1, SV2, Salmonella Enteritidis (SE) lipopolysaccharide (LPS), or water-oil-water emulsion (V). Local leukocyte levels and relative cytokine mRNA expression were monitored before (0 d) and at 6 h, 1 d, 2 d, 3 d, 5 d, and 7 d post-GF pulp injection (p.i.). Blood was collected through 28 d post-primary or -secondary vaccination, and SE-specific antibodies were quantified via ELISA.

RESULTS

Primary vaccine administration increased local heterophil and macrophage levels and increased IL-6 and IL-8 mRNA expressions at 6 h p.i., independent of treatment. Secondary administration extended these local immune activities through 3 d p.i. and included prolonged IL-17A mRNA expression. Primary and secondary GF-pulp injection with V resulted in rapid lymphocyte recruitment by 6 h p.i., comprised primarily of CD4+ and γδ T cells. SV1 and SV2 also produced a T-dependent systemic humoral immune response, as indicated by the IgM-to-IgG isotype switch, along with a memory phenotype in the secondary response.

CONCLUSIONS

These commercial-killed Salmonella vaccines, when prepared in water-oil-water emulsions, stimulated prolonged innate and T helper (Th) 17-type inflammatory responses at the injection site and produced a classic systemic humoral immune response after a second vaccination. Further research is needed to determine if extended inflammation influences adaptive immune responses in eliminating Salmonella infection.

Adjuvant-dependent impacts on vaccine-induced humoral responses and protection in preclinical models of nasal and genital colonization by pathogenic Neisseria

Neisseria gonorrhoeae, which causes the sexually transmitted infection gonorrhea and Neisseria meningitidis, a leading cause of bacterial meningitis and septicemia, are closely related human-restricted pathogens that inhabit distinct primary mucosal niches. While successful vaccines against invasive meningococcal disease have been available for decades, the rapid rise in antibiotic resistance has led to an urgent need to develop an effective gonococcal vaccine. Several surface antigens are shared among these two pathogens, making cross-species protection an exciting prospect. However, the type of vaccine-mediated immune response required to achieve protection against respiratory versus genital infection remains ill defined. In this study, we utilize well established mouse models of female lower genital tract colonization by N. gonorrhoeae and upper respiratory tract colonization by N. meningitidis to examine the performance of transferrin binding protein B (TbpB) vaccines formulated with immunologically distinct vaccine adjuvants. We demonstrate that vaccine-mediated protection is influenced by the choice of adjuvant, with Th1/2-balanced adjuvants performing optimally against N. gonorrhoeae, and both Th1/2-balanced and Th2-skewing adjuvants leading to a significant reduction in N. meningitidis burden. We further establish a lack of correlation between protection status and the humoral response or bactericidal titre. Combined, this work supports the feasibility for a single vaccine formulation to achieve pan-neisserial coverage.

Transcriptional Systems Vaccinology Approaches for Vaccine Adjuvant Profiling

Adjuvants are a diverse group of substances that can be added to vaccines to enhance antigen-specific immune responses and improve vaccine efficacy. The first adjuvants, discovered almost a century ago, were soluble crystals of aluminium salts. Over the following decades, oil emulsions, vesicles, oligodeoxynucleotides, viral capsids, and other complex organic structures have been shown to have adjuvant potential. However, the detailed mechanisms of how adjuvants enhance immune responses remain poorly understood and may be a barrier that reduces the rational selection of vaccine components. Previous studies on mechanisms of action of adjuvants have focused on how they activate innate immune responses, including the regulation of cell recruitment and activation, cytokine/chemokine production, and the regulation of some "immune" genes. This approach provides a narrow perspective on the complex events involved in how adjuvants modulate antigen-specific immune responses. A comprehensive and efficient way to investigate the molecular mechanism of action for adjuvants is to utilize systems biology approaches such as transcriptomics in so-called "systems vaccinology" analysis. While other molecular biology methods can verify if one or few genes are differentially regulated in response to vaccination, systems vaccinology provides a more comprehensive picture by simultaneously identifying the hundreds or thousands of genes that interact with complex networks in response to a vaccine. Transcriptomics tools such as RNA sequencing (RNA-Seq) allow us to simultaneously quantify the expression of practically all expressed genes, making it possible to make inferences that are only possible when considering the system as a whole. Here, we review some of the challenges in adjuvant studies, such as predicting adjuvant activity and toxicity when administered alone or in combination with antigens, or classifying adjuvants in groups with similar properties, while underscoring the significance of transcriptomics in systems vaccinology approaches to propel vaccine development forward.

SpiN-Tec: A T cell-based recombinant vaccine that is safe, immunogenic, and shows high efficacy in experimental models challenged with SARS-CoV-2 variants of concern

The emergence of new SARS-CoV-2 variants of concern associated with waning immunity induced by natural infection or vaccines currently in use suggests that the COVID-19 pandemic will become endemic. Investing in new booster vaccines using different platforms is a promising way to enhance protection and keep the disease under control. Here, we evaluated the immunogenicity, efficacy, and safety of the SpiN-Tec vaccine, based on a chimeric recombinant protein (SpiN) adjuvanted with CTVad1 (MF59-based adjuvant), aiming at boosting immunity against variants of concern of SARS-CoV-2. Immunization of K18-hACE-2 transgenic mice and hamsters induced high antibody titers and cellular immune response to the SpiN protein as well as to its components, RBD and N proteins. Importantly in a heterologous prime/boost protocol with a COVID-19 vaccine approved for emergency use (ChAdOx1), SpiN-Tec enhanced the level of circulation neutralizing antibodies (nAb). In addition to protection against the Wuhan isolate, protection against the Delta and Omicron variants was also observed as shown by reduced viral load and lung pathology. Toxicity and safety tests performed in rats demonstrated that the SpiN-Tec vaccine was safe and, based on these results, the SpiN-Tec phase I/II clinical trial was approved.

Microparticle and nanoparticle-based influenza vaccines

Influenza infections are a health public problem worldwide every year with the potential to become the next pandemic. Vaccination is the most effective strategy to prevent future influenza outbreaks, however, influenza vaccines need to be reformulated each year to provide protection due to viral antigenic drift and shift. As more efficient influenza vaccines are needed, it is relevant to recapitulate strategies to improve the immunogenicity and broad reactivity of the current vaccines. Here, we review the current approved vaccines in the U.S. market and the platform used for their production. We discuss the different approaches to develop a broadly reactive vaccine as well as reviewing the adjuvant systems that are under study for being potentially included in future influenza vaccine formulations. The main components of the immune system involved in achieving a protective immune response are reviewed and how they participate in the trafficking of particles systemically and in the mucosa. Finally, we describe and classify, according to their physicochemical properties, some of the potential micro and nano-particulate platforms that can be used as delivery systems for parenteral and mucosal vaccinations.

Recent Advances in the Development of Mincle-Targeting Vaccine Adjuvants

The Macrophage-inducible C-type lectin (Mincle) is a pattern-recognition receptor (PRR), which has shown much promise as a molecular target for the development of TH1/TH17-skewing vaccine adjuvants. In 2009, the first non-proteinaceous Mincle ligands, trehalose dimycolate (TDM) and trehalose dibehenate (TDB), were identified. This prompted a search for other Mincle agonists and the exploration of Mincle agonists as vaccine adjuvants for both preventative and therapeutic (anti-cancer) vaccines. In this review, we discuss those classes of Mincle agonists that have been explored for their adjuvant potential. These Mincle agonists have been used as stand-alone adjuvants or in combination with other pathogen-associated molecular patterns (PAMPs) or immunomodulatory agents. We will also highlight recently identified Mincle ligands with hitherto unknown adjuvanticity. Conjugate vaccines that contain covalently linked adjuvants and/or adjuvant-antigen combinations are also presented, as well as the different formulations (e.g., oil-in-water emulsions, liposomes, and particulate delivery systems) that have been used for the codelivery of antigens and adjuvants. Insofar the reader is presented with a thorough review of the potential of Mincle-mediated vaccine adjuvants, including historical context, present-day research and clinical trials, and outstanding research questions, such as the role of ligand presentation and Mincle clustering, which, if better understood, will aid in the development of the much-needed TH1/TH17-skewing vaccine adjuvants.

MINCLE and TLR9 agonists synergize to induce Th1/Th17 vaccine memory and mucosal recall in mice and non-human primates

Development of new vaccines tailored for difficult-to-target diseases is hampered by a lack of diverse adjuvants for human use, and none of the currently available adjuvants induce Th17 cells. Here, we develop a liposomal adjuvant, CAF®10b, that incorporates Mincle and Toll-like receptor 9 agonists. In parallel mouse and non-human primate studies comparing to CAF® adjuvants already in clinical trials, we report species-specific effects of adjuvant composition on the quality and magnitude of the responses. When combined with antigen, CAF®10b induces Th1 and Th17 responses and protection against a pulmonary infection with Mycobacterium tuberculosis in mice. In non-human primates, CAF®10b induces higher Th1 responses and robust Th17 responses detectable after six months, and systemic and pulmonary Th1 and Th17 recall responses, in a sterile model of local recall. Overall, CAF®10b drives robust memory antibody, Th1 and Th17 vaccine-responses via a non-mucosal immunization route across both rodent and primate species.

Use of 3M-052-AF with Alum adjuvant in HIV trimer vaccine induces human autologous neutralizing antibodies

Stabilized trimers preserving the native-like HIV envelope structure may be key components of a preventive HIV vaccine regimen to induce broadly neutralizing antibodies (bnAbs). We evaluated trimeric BG505 SOSIP.664 gp140 formulated with a novel TLR7/8 signaling adjuvant, 3M-052-AF/Alum, for safety, adjuvant dose-finding, and immunogenicity in a first-in-healthy adult (n = 17), randomized, and placebo-controlled trial (HVTN 137A). The vaccine regimen appeared safe. Robust, trimer-specific antibody, and B cell and CD4+ T cell responses emerged after vaccination. Five vaccinees developed serum autologous tier 2 nAbs (ID50 titer, 1:28-1:8647) after two to three doses targeting C3/V5 and/or V1/V2/V3 Env regions by electron microscopy and mutated pseudovirus-based neutralization analyses. Trimer-specific, B cell-derived monoclonal antibody activities confirmed these results and showed weak heterologous neutralization in the strongest responder. Our findings demonstrate the clinical utility of the 3M-052-AF/Alum adjuvant and support further improvements of trimer-based Env immunogens to focus responses on multiple broad nAb epitopes.

CT584 Is Not a Protective Vaccine Antigen against Respiratory Chlamydial Challenge in Mice

Background:Chlamydia trachomatis is the most prevalent bacterial sexually transmitted pathogen in humans worldwide. Since chlamydial infection is largely asymptomatic with the potential for serious complications, a preventative vaccine is likely the most viable long-term answer to this public health threat. Cell-free protein synthesis (CFPS) utilizes the cellular protein manufacturing machinery decoupled from the requirement for maintaining cellular viability, offering the potential for flexible, rapid, and decentralized production of recombinant protein vaccine antigens. Methods: Here, we use CFPS to produce the full-length putative chlamydial type three secretion system (T3SS) needle-tip protein, CT584, for evaluation as a vaccine antigen in mouse models. High-speed atomic force microscopy (HS-AFM) (RIBM, Tsukuba, Japan) imaging and computer simulations confirm that CFPS-produced CT584 retains a native-like structure prior to immunization. Female mice were primed with CT584 adjuvanted with CpG-1826 intranasally (i.n.) or CpG-1826 + Montanide ISA 720 intramuscularly (i.m.), followed four weeks later by an i.m. boost before respiratory challenge with 104 inclusion forming units (IFU) of Chlamydia muridarum. Results: Immunization with CT584 generated robust antibody responses but weak cell-mediated immunity and failed to protect against i.n. challenge as demonstrated by body weight loss, increased lung weights, and the presence of high numbers of IFUs in the lungs. Conclusion: While CT584 was not a protective vaccine candidate, the speed and flexibility with which CFPS can be used to produce other potential chlamydial antigens make it an attractive technique for antigen production.

Protection against experimental cryptococcosis elicited by Cationic Adjuvant Formulation 01-adjuvanted subunit vaccines

The fungal infection, cryptococcosis, is responsible for >100,000 deaths annually. No licensed vaccines are available. We explored the efficacy and immune responses of subunit cryptococcal vaccines adjuvanted with Cationic Adjuvant Formulation 01 (CAF01). CAF01 promotes humoral and T helper (Th) 1 and Th17 immune responses and has been safely used in human vaccine trials. Four subcutaneous vaccines, each containing single recombinant Cryptococcus neoformans protein antigens, partially protected mice from experimental cryptococcosis. Protection increased, up to 100%, in mice that received bivalent and quadrivalent vaccine formulations. Vaccinated mice that received a pulmonary challenge with C. neoformans had an influx of leukocytes into the lung including robust numbers of polyfunctional CD4+ T cells which produced interferon gamma (IFNγ), tumor necrosis factor alpha (TNFα), and interleukin (IL)-17 upon ex vivo antigenic stimulation. Cytokine-producing lung CD8+ T cells were also found, albeit in lesser numbers. A significant, durable IFNγ response was observed in the lungs, spleen, and blood. Moreover, IFNγ secretion following ex vivo stimulation directly correlated with fungal control in the lungs. Thus, we have developed multivalent cryptococcal vaccines which protect mice from experimental cryptococcosis using an adjuvant which has been safely tested in humans. These preclinical studies suggest a path towards human cryptococcal vaccine trials.

Mastoparan-7 adjuvanted COBRA H1 and H3 hemagglutinin influenza vaccines

Adjuvants enhance, prolong, and modulate immune responses by vaccine antigens to maximize protective immunity and enable more effective immunization in the young and elderly. Most adjuvants are formulated with injectable vaccines. However, an intranasal route of vaccination may induce mucosal and systemic immune responses for enhancing protective immunity in individuals and be easier to administer compared to injectable vaccines. In this study, a next generation of broadly-reactive influenza hemagglutinin (HA) vaccines were developed using the Computationally Optimized Broadly Reactive Antigen (COBRA) methodology. These HA vaccines were formulated with Mastoparan 7 (M7-NH2) mast cell degranulating peptide adjuvant and administered intranasally to determine vaccine-induced seroconversion of antibodies against a panel of influenza viruses and protection following infection with H1N1 and H3N2 viruses in mice. Mice vaccinated intranasally with M7-NH2-adjuvanted COBRA HA vaccines had high HAIs against a panel of H1N1 and H3N2 influenza viruses and were protected against both morbidity and mortality, with reduced viral lung titers, following challenge with an H1N1 influenza virus. Additionally, M7-NH2 adjuvanted COBRA HA vaccines induced Th2 skewed immune responses with robust IgG and isotype antibodies in the serum and mucosal lung lavages. Overall, this intranasally delivered M7-NH2 -adjuvanted COBRA HA vaccine provides effective protection against drifted H1N1 and H3N2 viruses.

Evaluation in mice of cell-free produced CT584 as a Chlamydia vaccine antigen

Chlamydia trachomatis is the most prevalent bacterial sexually transmitted pathogen worldwide. Since chlamydial infection is largely asymptomatic with the potential for serious complications, a preventative vaccine is likely the most viable long-term answer to this public health threat. Cell-free protein synthesis (CFPS) utilizes the cellular protein manufacturing machinery decoupled from the requirement for maintaining cellular viability, offering the potential for flexible, rapid, and de-centralized production of recombinant protein vaccine antigens. Here, we use CFPS to produce the putative chlamydial type three secretion system (T3SS) needle-tip protein, CT584, for use as a vaccine antigen in mouse models. High-speed atomic force microscopy (HS-AFM) imaging and computer simulations confirm that CFPS-produced CT584 retains a native-like structure prior to immunization. Female mice were primed with CT584 adjuvanted with CpG-1826 intranasally (i.n.) or CpG-1826 + Montanide ISA 720 intramuscularly (i.m.), followed four-weeks later by an i.m. boost before respiratory challenge with 104 inclusion forming units (IFU) of Chlamydia muridarum. Immunization with CT584 generated robust antibody responses but weak cell mediated immunity and failed to protect against i.n. challenge as demonstrated by body weight loss, increased lungs' weights and the presence of high numbers of IFUs in the lungs. While CT584 alone may not be the ideal vaccine candidate, the speed and flexibility with which CFPS can be used to produce other potential chlamydial antigens makes it an attractive technique for antigen production.

HIV BG505 SOSIP.664 trimer with 3M-052-AF/alum induces human autologous tier-2 neutralizing antibodies

Stabilized trimers preserving the native-like HIV envelope structure may be key components of a preventive HIV vaccine regimen to induce broadly neutralizing antibodies (bnAbs). We evaluated trimeric BG505 SOSIP.664 gp140, formulated with a novel TLR7/8 signaling adjuvant, 3M-052-AF/Alum, for safety, adjuvant dose-finding and immunogenicity in a first-in-healthy adult (n=17), randomized, placebo-controlled trial (HVTN 137A). The vaccine regimen appeared safe. Robust, trimer-specific antibody, B-cell and CD4+ T-cell responses emerged post-vaccination. Five vaccinees developed serum autologous tier-2 nAbs (ID50 titer, 1:28-1:8647) after 2-3 doses targeting C3/V5 and/or V1/V2/V3 Env regions by electron microscopy and mutated pseudovirus-based neutralization analyses. Trimer-specific, B-cell-derived monoclonal antibody activities confirmed these results and showed weak heterologous neutralization in the strongest responder. Our findings demonstrate the clinical utility of the 3M-052-AF/alum adjuvant and support further improvements of trimer-based Env immunogens to focus responses on multiple broad nAb epitopes.

KEY TAKEAWAY/TAKE-HOME MESSAGES

HIV BG505 SOSIP.664 trimer with novel 3M-052-AF/alum adjuvant in humans appears safe and induces serum neutralizing antibodies to matched clade A, tier 2 virus, that map to diverse Env epitopes with relatively high titers. The novel adjuvant may be an important mediator of vaccine response.

Feasibility of using a combination of staphylococcal superantigen-like proteins 3, 7 and 11 in a fusion vaccine for Staphylococcus aureus

Staphylococcus aureus is a significant bacterial pathogen in both community and hospital settings, and the escalation of antimicrobial-resistant strains is of immense global concern. Vaccination is an inviting long-term strategy to curb staphylococcal disease, but identification of an effective vaccine has proved to be challenging. Three well-characterized, ubiquitous, secreted immune evasion factors from the staphylococcal superantigen-like (SSL) protein family were selected for the development of a vaccine. Wild-type SSL3, 7 and 11, which inhibit signaling through Toll-like receptor 2, cleavage of complement component 5 and neutrophil function, respectively, were successfully combined into a stable, active fusion protein (PolySSL7311). Vaccination of mice with an attenuated form of the PolySSL7311 protein stimulated significantly elevated specific immunoglobulin G and splenocyte proliferation responses to each component relative to adjuvant-only controls. Vaccination with PolySSL7311, but not a mixture of the individual proteins, led to a > 102 reduction in S. aureus tissue burden compared with controls after peritoneal challenge. Comparable antibody responses were elicited after coadministration of the vaccine in either AddaVax (an analog of MF59) or an Alum-based adjuvant; but only AddaVax conferred a significant reduction in bacterial load, aligning with other studies that suggest both cellular and humoral immune responses are necessary for protective immunity to S. aureus. Anti-sera from mice immunized with PolySSL7311, but not individual proteins, partially neutralized the functional activities of SSL7. This study confirms the importance of these SSLs for the survival of S. aureus in vivo and suggests that PolySSL7311 is a promising vaccine candidate.

Protection against experimental cryptococcosis elicited by Cationic Adjuvant Formulation 01-adjuvanted subunit vaccines

The fungal infection, cryptococcosis, is responsible for >100,000 deaths annually. No licensed vaccines are available. We explored the efficacy and immune responses of subunit cryptococcal vaccines adjuvanted with Cationic Adjuvant Formulation 01 (CAF01). CAF01 promotes humoral and T helper (Th) 1 and Th17 immune responses and has been safely used in human vaccine trials. Four subcutaneous vaccines, each containing single recombinant Cryptococcus neoformans protein antigens, partially protected mice from experimental cryptococcosis. Protection increased, up to 100%, in mice that received bivalent and quadrivalent vaccine formulations. Vaccinated mice that received a pulmonary challenge with C. neoformans had an influx of leukocytes into the lung including robust numbers of polyfunctional CD4+ T cells which produced Interferon gamma (IFNγ), tumor necrosis factor alpha (TNFα), and interleukin (IL)-17 upon ex vivo antigenic stimulation. Cytokine-producing lung CD8+ T cells were also found, albeit in lesser numbers. A significant, durable IFNγ response was observed in the lungs, spleen, and blood. Moreover, IFNγ secretion following ex vivo stimulation directly correlated with fungal clearance in the lungs. Thus, we have developed multivalent cryptococcal vaccines which protect mice from experimental cryptococcosis using an adjuvant which has been safely tested in humans. These preclinical studies suggest a path towards human cryptococcal vaccine trials.

Vaccine adjuvants: Tailoring innate recognition to send the right message

Adjuvants play pivotal roles in vaccine development, enhancing immunization efficacy through prolonged retention and sustained release of antigen, lymph node targeting, and regulation of dendritic cell activation. Adjuvant-induced activation of innate immunity is achieved via diverse mechanisms: for example, adjuvants can serve as direct ligands for pathogen recognition receptors or as inducers of cell stress and death, leading to the release of immunostimulatory-damage-associated molecular patterns. Adjuvant systems increasingly stimulate multiple innate pathways to induce greater potency. Increased understanding of the principles dictating adjuvant-induced innate immunity will subsequently lead to programming specific types of adaptive immune responses. This tailored optimization is fundamental to next-generation vaccines capable of inducing robust and sustained adaptive immune memory across different cohorts.

Repeated immunization with ATRA-containing liposomal adjuvant transdifferentiates Th17 cells to a Tr1-like phenotype

In many autoimmune diseases, autoantigen-specific Th17 cells play a pivotal role in disease pathogenesis. Th17 cells can transdifferentiate into other T cell subsets in inflammatory conditions, however, there have been no attempts to target Th17 cell plasticity using vaccines. We investigated if autoantigen-specific Th17 cells could be specifically targeted using a therapeutic vaccine approach, where antigen was formulated in all-trans retinoic acid (ATRA)-containing liposomes, permitting co-delivery of antigen and ATRA to the same target cell. Whilst ATRA was previously found to broadly reduce Th17 responses, we found that antigen formulated in ATRA-containing cationic liposomes only inhibited Th17 cells in an antigen-specific manner and not when combined with an irrelevant antigen. Furthermore, this approach shifted existing Th17 cells away from IL-17A expression and transcriptomic analysis of sorted Th17 lineage cells from IL-17 fate reporter mice revealed a shift of antigen-specific Th17 cells to exTh17 cells, expressing functional markers associated with T cell regulation and tolerance. In the experimental autoimmune encephalomyelitis (EAE) mouse model of MS, vaccination with myelin-specific (MOG) antigen in ATRA-containing liposomes reduced Th17 responses and alleviated disease. This highlights the potential of therapeutic vaccination for changing the phenotype of existing Th17 cells in the context of immune mediated diseases.

BpOmpW antigen administered with CAF01 adjuvant stimulates comparable T cell responses to Sigma adjuvant system

There are no licensed vaccines to protect vulnerable populations from the potentially fatal tropical infection, melioidosis, despite its causative agent, Burkholderia pseudomallei, being endemic in tropical and subtropical regions. A promising vaccine candidate, BpOmpW protected mice from melioidosis infection for up to 81 days and stimulated robust interferon gamma responses in CD4+, CD8+, NK and NKT cells. In order to progress to human studies, selection of an adjuvant with an acceptable human safety profile that stimulates appropriate correlates of protection is essential. Here we demonstrate that the CAF01 vaccine adjuvant elicits optimal immune correlates of protection when administered with our BpOmpW vaccine. Specifically, we demonstrate that CAF01 administered with BpOmpW elicits robust Th1 responses, with potent IFN-γ responses in CD4+ and CD8+ T cells and NKT cells, in addition to Th17 and Th2 responses. This formulation will be particularly effective in protecting susceptible populations including people with type 2 diabetes from melioidosis.

Tuberculosis vaccine developments and efficient delivery systems: A comprehensive appraisal

Despite the widespread use of the Bacillus Calmette-Guérin (BCG) vaccine, Mycobacterium tuberculosis (MTB) continues to be a global burden. Vaccination has been proposed to prevent and treat tuberculosis (TB) infection, and several of them are in different phases of clinical trials. Though vaccine production is in progress but requires more attention. There are several TB vaccines in the trial phase, most of which are based on a combination of proteins/adjuvants or recombinant viral vectors used for selected MTB antigens. In this review, we attempted to discuss different types of TB vaccines based on the vaccine composition, the immune responses generated, and their clinical trial phases. Furthermore, we have briefly overviewed the effective delivery systems used for the TB vaccine and their effectiveness in different vaccines.

Immune signature of Chlamydia vaccine CTH522/CAF®01 translates from mouse-to-human and induces durable protection in mice

The clinical development of an effective Chlamydia vaccine requires in-depth understanding of how well protective pre-clinical immune signatures translate to humans. Here, we report a comparative immunological characterization of CTH522/CAF®01 in female mice and humans. We find a range of immune signatures that translate from mouse to human, including a Th1/Th17 cytokine profile and antibody functionality. We identify vaccine-induced T cell epitopes, conserved among Chlamydia serovars, and previously found in infected individuals. Using the mouse model, we show that the common immune signature protected against ascending infection in mice, and vaccine induced antibodies could delay bacterial ascension to the oviduct, as well as development of pathology, in a T cell depleted mouse model. Finally, we demonstrate long-lasting immunity and protection of mice one year after vaccination. Based on the results obtained in the present study, we propose to further investigate CTH522/CAF®01 in a phase IIb study.

Immunomodulatory Peptides as Vaccine Adjuvants and Antimicrobial Agents

The underdevelopment of adjuvant discovery and diversity, compared to core vaccine technology, is evident. On the other hand, antibiotic resistance is on the list of the top ten threats to global health. Immunomodulatory peptides that target a pathogen and modulate the immune system simultaneously are promising for the development of preventive and therapeutic molecules. Since investigating innate immunity in insects has led to prominent achievements in human immunology, such as toll-like receptor (TLR) discovery, we used the capacity of the immunomodulatory peptides of arthropods with concomitant antimicrobial or antitumor activity. An SVM-based machine learning classifier identified short immunomodulatory sequences encrypted in 643 antimicrobial peptides from 55 foe-to-friend arthropods. The critical features involved in efficacy and safety were calculated. Finally, 76 safe immunomodulators were identified. Then, molecular docking and simulation studies defined the target of the most optimal peptide ligands among all human cell-surface TLRs. SPalf2-453 from a crab is a cell-penetrating immunoadjuvant with antiviral properties. The peptide interacts with the TLR1/2 heterodimer. SBsib-711 from a blackfly is a TLR4/MD2 ligand used as a cancer vaccine immunoadjuvant. In addition, SBsib-711 binds CD47 and PD-L1 on tumor cells, which is applicable in cancer immunotherapy as a checkpoint inhibitor. MRh4-679 from a shrimp is a broad-spectrum or universal immunoadjuvant with a putative Th1/Th2-balanced response. We also implemented a pathway enrichment analysis to define fingerprints or immunological signatures for further in vitro and in vivo immunogenicity and reactogenicity measurements. Conclusively, combinatorial machine learning, molecular docking, and simulation studies, as well as systems biology, open a new opportunity for the discovery and development of multifunctional prophylactic and therapeutic lead peptides.

Vaccine development: Current trends and technologies

Despite the effectiveness of vaccination in reducing or eradicating diseases caused by pathogens, there remain certain diseases and emerging infections for which developing effective vaccines is inherently challenging. Additionally, developing vaccines for individuals with compromised immune systems or underlying medical conditions presents significant difficulties. As well as traditional vaccine different methods such as inactivated or live attenuated vaccines, viral vector vaccines, and subunit vaccines, emerging non-viral vaccine technologies, including viral-like particle and nanoparticle vaccines, DNA/RNA vaccines, and rational vaccine design, offer new strategies to address the existing challenges in vaccine development. These advancements have also greatly enhanced our understanding of vaccine immunology, which will guide future vaccine development for a broad range of diseases, including rapidly emerging infectious diseases like COVID-19 and diseases that have historically proven resistant to vaccination. This review provides a comprehensive assessment of emerging non-viral vaccine production methods and their application in addressing the fundamental and current challenges in vaccine development.

Co-adjuvanting DDA/TDB liposomes with a TLR7 agonist allows for IgG2a/c class-switching in the absence of Th1 cells

Class-switching to IgG2a/c in mice is a hallmark response to intracellular pathogens. T cells can promote class-switching and the predominant pathway for induction of IgG2a/c antibody responses has been suggested to be via stimulation from Th1 cells. We previously formulated CAF®01 (cationic liposomes containing dimethyldioctadecylammonium bromide (DDA) and Trehalose-6,6-dibehenate (TDB)) with the lipidated TLR7/8 agonist 3M-052 (DDA/TDB/3M-052), which promoted robust Th1 immunity in newborn mice. When testing this adjuvant in adult mice using the recombinant Chlamydia trachomatis (C.t.) vaccine antigen CTH522, it similarly enhanced IgG2a/c responses compared to DDA/TDB, but surprisingly reduced the magnitude of the IFN-γ+Th1 response in a TLR7 agonist dose-dependent manner. Single-cell RNA-sequencing revealed that DDA/TDB/3M-052 liposomes initiated early transcription of class-switch regulating genes directly in pre-germinal center B cells. Mixed bone marrow chimeras further demonstrated that this adjuvant did not require Th1 cells for IgG2a/c switching, but rather facilitated TLR7-dependent T-bet programming directly in B cells. This study underlines that adjuvant-directed IgG2a/c class-switching in vivo can occur in the absence of T-cell help, via direct activation of TLR7 on B cells and positions DDA/TDB/3M-052 as a powerful adjuvant capable of eliciting type I-like immunity in B cells without strong induction of Th1 responses.

Head-to-Head Comparison of Novel Vaccine Technologies Comes with a Minefield of Challenges

Modern vaccine development is having a golden period, with a variety of novel subunit technologies being introduced into clinical development in recent years. This opens the opportunity to find the best platform to use for novel vaccine antigen candidates through head-to-head comparative studies. Seldom appreciated is, however, the fact that these different technologies often do not have the same optimal antigen dose ratio, prime-boost regime and peak timepoint for measuring immunity. Instead, the preclinical studies that make the basis for platform selection use standard protocols not optimized for individual vaccines and fail to make selection on an informed basis. Here, I discuss the opportunities we have to optimize vaccine platform technologies through a better understanding of vaccine priming kinetics, the optimal antigen dose and sampling time and location.

A CAF01-adjuvanted whole asexual blood-stage liposomal malaria vaccine induces a CD4+ T-cell-dependent strain-transcending protective immunity in rodent models

IMPORTANCE

Malaria is a devastating disease that has claimed many lives, especially children <5 years of age in Sub-Saharan Africa, as documented in World Malaria Reports by WHO. Even though vector control and chemoprevention tools have helped with elimination efforts in some, if not all, endemic areas, these efforts have been hampered by serious issues (including drug and insecticide resistance and disruption to social cohesion caused by the COVID-19 pandemic). Development of an effective malaria vaccine is the alternative preventative tool in the fight against malaria. Vaccines save millions of lives each year and have helped in elimination and/or eradication of global diseases. Development of a highly efficacious malaria vaccine that will ensure long-lasting protective immunity will be a "game-changing" prevention strategy to finally eradicate the disease. Such a vaccine will need to counteract the significant obstacles that have been hampering subunit vaccine development to date, including antigenic polymorphism, sub-optimal immunogenicity, and waning vaccine efficacy.

Reconstituted dry powder formulations of ZnO-adjuvanted ovalbumin induce equivalent antigen specific antibodies but lower T cell responses than ovalbumin adjuvanted with Alhydrogel® or cationic adjuvant formulation 01 (CAF®01)

Most licensed human vaccines are based on liquid dosage forms but have poor storage stability and require continuous and expensive cold-chain storage. In contrast, the use of solid vaccine dosage forms produced by for example spray drying, extends shelf life and eliminates the need for a cold chain. Zinc oxide (ZnO)-based nanoparticles display immunomodulatory properties, but their adjuvant effect as a dry powder formulation is unknown. Here, we show that reconstituted dry powder formulations of ZnO particles containing the model antigen ovalbumin (OVA) induce antigen-specific CD8+ T-cell and humoral responses. By systematically varying the ratio between ZnO and mannitol during spray drying, we manufactured dry powder formulations of OVA-containing ZnO particles that displayed: (i) a spherical or wrinkled surface morphology, (ii) an aerodynamic diameter and particle size distribution optimal for deep lung deposition, and (iii) aerosolization properties suitable for lung delivery. Reconstituted dry powder formulations of ZnO particles were well-tolerated by Calu-3 lung epithelial cells. Furthermore, almost equivalent OVA-specific serum antibody responses were stimulated by reconstituted ZnO particles, OVA adjuvanted with Alhydrogel®, and OVA adjuvanted with the cationic adjuvant formulation 01 (CAF®01). However, reconstituted dry powder ZnO particles and OVA adjuvanted with Alhydrogel® induced significantly lower OVA-specific CD8+CD44+ T-cell responses in the spleen than OVA adjuvanted with CAF®01. Similarly, reconstituted dry powder ZnO particles activated significantly lower percentages of follicular helper T cells and germinal center B cells in the draining lymph nodes than OVA adjuvanted with CAF®01. Overall, our results show that reconstituted dry powder formulations of ZnO nanoparticles can induce antigen-specific antibodies and can be used in vaccines to enhance antigen-specific humoral immune responses against subunit protein antigens.

Nanotechnology Platform for Advancing Vaccine Development against the COVID-19 Virus

The COVID-19 pandemic has had a profound impact on societies, public health, healthcare systems, and the world economy. With over 771 million people infected worldwide and a staggering death toll exceeding 6,960,783 as of 4 October 2023 (according to the World Health Organization), the urgency for a solution was paramount. Since the outbreak, the demand for immediate treatment for COVID-19 viral infection, as well as for effective vaccination against this virus, was soaring, which led scientists, pharmaceutical/biotech companies, government health agencies, etc., to think about a treatment strategy that could control and minimize this outbreak as soon as possible. Vaccination emerged as the most effective strategy to combat this infectious disease. For vaccination strategies, any conventional vaccine approach using attenuated live or inactivated/engineered virus, as well as other approaches, typically requires years of research and assessment. However, the urgency of the situation promoted a faster and more effective approach to vaccine development against COVID-19. The role of nanotechnology in designing, manufacturing, boosting, and delivering vaccines to the host to counter this virus was unquestionably valued and assessed. Several nanoformulations are discussed here in terms of their composition, physical properties, credibility, and applications in past vaccine development (as well as the possibility of using those used in previous applications for the generation of the COVID-19 vaccine). Controlling and eliminating the spread of the virus and preventing future recurrence requires a safe, tolerable, and effective vaccine strategy. In this review, we discuss the potential of nanoformulations as the basis for an effective vaccine strategy against COVID-19.

Evaluation of three formulations based on Polymorphic membrane protein D in mice infected with Chlamydia trachomatis

The significant impact of Chlamydia trachomatis(Ct) infections worldwide highlights the need to develop a prophylactic vaccine that elicits effective immunity and protects the host from the immunopathological effects of Ct infection. The aim of this study was to evaluate a vaccine based on a fragment of the Polymorphic membrane protein D (FPmpD) of C. trachomatis as an immunogen using a heterologous DNA prime-protein boost strategy in female mice Three different formulations were evaluated as protein boost: free recombinant FPmpD (rFPmpD) or rFPmpD formulated with a liposomal adjuvant alternatively supplemented with CpG or a cationic gemini lipopeptide as immunostimulants. The three candidates induced an increase in the cervicovaginal and systemic titers of anti-rFPmpD antibodies in two strains of mice (BALB/c and C57BL/6), with no evidence of fertility alterations. The three formulations induced a rapid and robust humoral immune response upon the Ct challenge. However, the booster with free rFPmpD more efficiently reduced the shedding of infective Ct and prevented the development of immunopathology. The formulations containing adjuvant induced a strong inflammatory reaction in the uterine tissue. Hence, the prime-boost strategy with the adjuvant-free FPmpD vaccine formulation might constitute a promissory candidate to prevent C. trachomatis intravaginal infection.

Method of manufacturing CAF®09 liposomes affects immune responses induced by adjuvanted subunit proteins

The ability to induce antigen-specific CD4+ and CD8+T-cell responses is one of the fundamental requirements when developing new efficacious vaccines against challenging infectious diseases and cancer. However, no adjuvants are currently approved for human subunit vaccines that induce T-cell immunity. Here, we incorporated a Toll-like receptor 4 agonist, i.e., the ionizable lipidoid L5N12, in the liposomal cationic adjuvant formulation 09 (CAF®09), and found that modified CAF®09 liposomes possess preserved adjuvant function as compared to unmodified CAF®09. CAF®09 consists of the cationic lipid dimethyldioctadecylammonium (DDA), monomycoloyl glycerol analogue 1 (MMG-1), and polyinosinic:polycytidylic acid [poly(I:C)]. By using the microfluidic mixing technology for liposome preparation, we gradually replaced DDA with L5N12, while keeping the molar ratios of MMG-1 and poly(I:C) constant. We found that this type of modification resulted in colloidally stable liposomes, which were significantly smaller and displayed reduced surface charge as compared to unmodified CAF®09, prepared by using the conventional thin film method. We showed that incorporation of L5N12 decreases the membrane rigidity of CAF®09 liposomes. Furthermore, vaccination with antigen adjuvanted with L5N12-modified CAF®09 or antigen adjuvanted with unmodified CAF®09, respectively, induced comparable antigen-specific serum antibody titers. We found that antigen adjuvanted with L5N12-modified CAF®09 induced antigen-specific effector and memory CD4+ and CD8+T-cell responses in the spleen comparable to those induced when unmodified CAF®09 was used as adjuvant. However, incorporating L5N12 did not have a synergistic immunopotentiating effect on the antibody and T-cell responses induced by CAF®09. Moreover, vaccination with antigen adjuvanted with unmodified CAF®09, which was manufactured by using microfluidic mixing, induced significantly lower antigen-specific CD4+ and CD8+T-cell responses than vaccination with antigen adjuvanted with unmodified CAF®09, which was prepared by using the thin film method. These results show that the method of manufacturing affects CAF®09 liposome adjuvanted antigen-specific immune responses, which should be taken into consideration when evaluating immunogenicity of subunit protein vaccines.

Post-fusion influenza vaccine adjuvanted with SA-2 confers heterologous protection via Th1-polarized, non-neutralizing antibody responses

Development of a universal influenza vaccine that can provide robust and long-lasting protection against heterologous infections is a global public health priority. A variety of vaccine antigens are designed to increase the antigenicity of conserved epitopes to elicit cross-protective antibodies that often lack virus-neutralizing activity. Given the contribution of antibody effector functions to cross-protection, adjuvants need to be added to modulate antibody effector functions as well as to enhance antibody quantity. We previously showed that post-fusion influenza vaccine antigens elicit non-neutralizing but cross-protective antibodies against conserved epitopes. Here, using a murine model, we comparably assessed the adjuvanticity of the newly developed SA-2 adjuvant containing a synthetic TLR7 agonist DSP-0546 and squalene-based MF59 analog as representative Th1- or Th2-type adjuvants, respectively. Both types of adjuvants in the post-fusion vaccine comparably enhanced cross-reactive IgG titers against heterologous strains. However, only SA-2 skewed the IgG subclass into the IgG2c subclass in association to its Th1-polarizing nature. SA-2-enhanced IgG2c responses exhibited antibody-dependent cellular cytotoxicity against heterologous virus strains, without cross-neutralizing activity. Eventually, the SA-2-adjuvanted vaccination provided protection against lethal infection by heterologous H3N2 and H1N1 viruses. Together, we conclude that the combination with a SA-2 is advantageous for enhancing the cross-protective capability of post-fusion HA vaccines that elicit non-neutralizing IgG antibodies.

Self-Adjuvanting Calcium-Phosphate-Coated Microcrystal-Based Vaccines Induce Pyroptosis in Human and Livestock Immune Cells

Successful vaccines require adjuvants able to activate the innate immune system, eliciting antigen-specific immune responses and B-cell-mediated antibody production. However, unwanted secondary effects and the lack of effectiveness of traditional adjuvants has prompted investigation into novel adjuvants in recent years. Protein-coated microcrystals modified with calcium phosphate (CaP-PCMCs) in which vaccine antigens are co-immobilised within amino acid crystals represent one of these promising self-adjuvanting vaccine delivery systems. CaP-PCMCs has been shown to enhance antigen-specific IgG responses in mouse models; however, the exact mechanism of action of these microcrystals is currently unclear. Here, we set out to investigate this mechanism by studying the interaction between CaP-PCMCs and mammalian immune cells in an in vitro system. Incubation of cells with CaP-PCMCs induced rapid pyroptosis of peripheral blood mononuclear cells and monocyte-derived dendritic cells from cattle, sheep and humans, which was accompanied by the release of interleukin-1β and the activation of Caspase-1. We show that this pyroptotic event was cell-CaP-PCMCs contact dependent, and neither soluble calcium nor microcrystals without CaP (soluble PCMCs) induced pyroptosis. Our results corroborate CaP-PCMCs as a promising delivery system for vaccine antigens, showing great potential for subunit vaccines where the enhancement or find tuning of adaptive immunity is required.

Polyfunctional antibodies: a path towards precision vaccines for vulnerable populations

Vaccine efficacy determined within the controlled environment of a clinical trial is usually substantially greater than real-world vaccine effectiveness. Typically, this results from reduced protection of immunologically vulnerable populations, such as children, elderly individuals and people with chronic comorbidities. Consequently, these high-risk groups are frequently recommended tailored immunisation schedules to boost responses. In addition, diverse groups of healthy adults may also be variably protected by the same vaccine regimen. Current population-based vaccination strategies that consider basic clinical parameters offer a glimpse into what may be achievable if more nuanced aspects of the immune response are considered in vaccine design. To date, vaccine development has been largely empirical. However, next-generation approaches require more rational strategies. We foresee a generation of precision vaccines that consider the mechanistic basis of vaccine response variations associated with both immunogenetic and baseline health differences. Recent efforts have highlighted the importance of balanced and diverse extra-neutralising antibody functions for vaccine-induced protection. However, in immunologically vulnerable populations, significant modulation of polyfunctional antibody responses that mediate both neutralisation and effector functions has been observed. Here, we review the current understanding of key genetic and inflammatory modulators of antibody polyfunctionality that affect vaccination outcomes and consider how this knowledge may be harnessed to tailor vaccine design for improved public health.

A protective, single-visit TB vaccination regimen by co-administration of a subunit vaccine with BCG

The only licensed tuberculosis (TB) vaccine, Bacillus Calmette Guerin (BCG), fails to reliably protect adolescents and adults from pulmonary TB, resulting in ~1.6 million deaths annually. Protein subunit vaccines have shown promise against TB in clinical studies. Unfortunately, most subunit vaccines require multiple administrations, which increases the risk of loss to follow-up and necessitates more complex and costly logistics. Given the well-documented adjuvant effect of BCG, we hypothesized that BCG co-administration could compensate for a reduced number of subunit vaccinations. To explore this, we developed an expression-optimized version of our H107 vaccine candidate (H107e), which does not cross-react with BCG. In the CAF®01 adjuvant, a single dose of H107e induced inferior protection compared to three H107e/CAF®01 administrations. However, co-administering a single dose of H107e/CAF®01 with BCG significantly improved protection, which was equal to BCG co-administered with three H107e/CAF®01 doses. Importantly, combining BCG with a single H107e/CAF®01 dose also increased protection in previously BCG-primed animals. Overall, a single dose of H107e/CAF®01 with BCG induced long-lived immunity and triggered BCG-specific Th17 responses. These data support co-administration of BCG and subunit vaccines in both BCG naïve and BCG-primed individuals as an improved TB vaccine strategy with reduced number of vaccination visits.

SARS-CoV-2 RBD Conjugated to Polyglucin, Spermidine, and dsRNA Elicits a Strong Immune Response in Mice

Despite the rapid development and approval of several COVID vaccines based on the full-length spike protein, there is a need for safe, potent, and high-volume vaccines. Considering the predominance of the production of neutralizing antibodies targeting the receptor-binding domain (RBD) of S-protein after natural infection or vaccination, it makes sense to choose RBD as a vaccine immunogen. However, due to its small size, RBD exhibits relatively poor immunogenicity. Searching for novel adjuvants for RBD-based vaccine formulations is considered a good strategy for enhancing its immunogenicity. Herein, we assess the immunogenicity of severe acute respiratory syndrome coronavirus 2 RBD conjugated to a polyglucin:spermidine complex (PGS) and dsRNA (RBD-PGS + dsRNA) in a mouse model. BALB/c mice were immunized intramuscularly twice, with a 2-week interval, with 50 µg of RBD, RBD with Al(OH)₃, or conjugated RBD. A comparative analysis of serum RBD-specific IgG and neutralizing antibody titers showed that PGS, PGS + dsRNA, and Al(OH)₃ enhanced the specific humoral response in animals. There was no significant difference between the groups immunized with RBD-PGS + dsRNA and RBD with Al(OH)₃. Additionally, the study of the T-cell response in animals showed that, unlike adjuvants, the RBD-PGS + dsRNA conjugate stimulates the production of specific CD4+ and CD8+ T cells in animals.

Different configurations of SARS-CoV-2 spike protein delivered by integrase-defective lentiviral vectors induce persistent functional immune responses, characterized by distinct immunogenicity profiles

Several COVID-19 vaccine strategies utilizing new formulations for the induction of neutralizing antibodies (nAbs) and T cell immunity are still under evaluation in preclinical and clinical studies. Here we used Simian Immunodeficiency Virus (SIV)-based integrase defective lentiviral vector (IDLV) delivering different conformations of membrane-tethered Spike protein in the mouse immunogenicity model, with the aim of inducing persistent nAbs against multiple SARS-CoV-2 variants of concern (VoC). Spike modifications included prefusion-stabilizing double proline (2P) substitutions, mutations at the furin cleavage site (FCS), D614G mutation and truncation of the cytoplasmic tail (delta21) of ancestral and Beta (B.1.351) Spike, the latter mutation to markedly improve IDLV membrane-tethering. BALB/c mice were injected once with IDLV delivering the different forms of Spike or the recombinant trimeric Spike protein with 2P substitutions and FCS mutations in association with a squalene-based adjuvant. Anti-receptor binding domain (RBD) binding Abs, nAbs and T cell responses were detected up to six months from a single immunization with escalating doses of vaccines in all mice, but with different levels and kinetics. Results indicated that IDLV delivering the Spike protein with all the combined modifications, outperformed the other candidates in terms of T cell immunity and level of both binding Abs and nAbs soon after the single immunization and persistence over time, showing the best capacity to neutralize all formerly circulating VoC Alpha, Beta, Gamma and Delta. Although present, the lowest response was detected against Omicron variants (BA.1, BA.2 and BA.4/5), suggesting that the magnitude of immune evasion may be related to the higher genetic distance of Omicron as indicated by increased number of amino acid substitutions in Spike acquired during virus evolution.

C-type lectin receptor agonists elicit functional IL21-expressing Tfh cells and induce primary B cell responses in neonates

Introduction

C-type lectin receptor (CLR) agonists emerged as superior inducers of primary B cell responses in early life compared with Toll-like receptor (TLR) agonists, while both types of adjuvants are potent in adults.

Methods

Here, we explored the mechanisms accounting for the differences in neonatal adjuvanticity between a CLR-based (CAF®01) and a TLR4-based (GLA-SE) adjuvant administered with influenza hemagglutinin (HA) in neonatal mice, by using transcriptomics and systems biology analyses.

Results

On day 7 after immunization, HA/CAF01 increased IL6 and IL21 levels in the draining lymph nodes, while HA/GLA-SE increased IL10. CAF01 induced mixed Th1/Th17 neonatal responses while T cell responses induced by GLA-SE had a more pronounced Th2-profile. Only CAF01 induced T follicular helper (Tfh) cells expressing high levels of IL21 similar to levels induced in adult mice, which is essential for germinal center (GC) formation. Accordingly, only CAF01- induced neonatal Tfh cells activated adoptively transferred hen egg lysozyme (HEL)-specific B cells to form HEL+ GC B cells in neonatal mice upon vaccination with HEL-OVA.

Discussion

Collectively, the data show that CLR-based adjuvants are promising neonatal and infant adjuvants due to their ability to harness Tfh responses in early life.

A novel adjuvant formulation induces robust Th1/Th17 memory and mucosal recall responses in Non-Human Primates

After clean drinking water, vaccination is the most impactful global health intervention. However, development of new vaccines against difficult-to-target diseases is hampered by the lack of diverse adjuvants for human use. Of particular interest, none of the currently available adjuvants induce Th17 cells. Here, we develop and test an improved liposomal adjuvant, termed CAF®10b, that incorporates a TLR-9 agonist. In a head-to-head study in non-human primates (NHPs), immunization with antigen adjuvanted with CAF®10b induced significantly increased antibody and cellular immune responses compared to previous CAF® adjuvants, already in clinical trials. This was not seen in the mouse model, demonstrating that adjuvant effects can be highly species specific. Importantly, intramuscular immunization of NHPs with CAF®10b induced robust Th17 responses that were observed in circulation half a year after vaccination. Furthermore, subsequent instillation of unadjuvanted antigen into the skin and lungs of these memory animals led to significant recall responses including transient local lung inflammation observed by Positron Emission Tomography-Computed Tomography (PET-CT), elevated antibody titers, and expanded systemic and local Th1 and Th17 responses, including >20% antigen-specific T cells in the bronchoalveolar lavage. Overall, CAF®10b demonstrated an adjuvant able to drive true memory antibody, Th1 and Th17 vaccine-responses across rodent and primate species, supporting its translational potential.

Pulmonary Administration of the Liposome-Based Adjuvant CAF01: Effect of Surface Charge on Mucosal Adjuvant Function

Mucosal surfaces of the lungs represent a major site of entry for airborne pathogens, and pulmonary administration of vaccines is an attractive strategy to induce protective mucosal immunity in the airways. Recently, we demonstrated the potential of pulmonary vaccination with the tuberculosis subunit antigen H56 adjuvanted with the cationic liposomal adjuvant formulation CAF01, which consists of the cationic lipid dimethyldioctadecylammonium (DDA) bromide and the synthetic cord factor trehalose-6,6'-dibehenate. However, the cationic charge of DDA represents a major safety challenge. Hence, replacing DDA with a safer zwitterionic or anionic phospholipid is an attractive approach to improve vaccine safety, but the effect of liposomal surface charge on the induction of mucosal immunity after airway immunization is poorly understood. Here, we investigated the effect of surface charge by replacing the cationic DDA component of CAF01 with zwitterionic dipalmitoylphosphatidylcholine (DPPC) or anionic dipalmitoylphosphatidylglycerol (DPPG), and we show that charge modification enhances antigen-specific pulmonary T-cell responses against co-formulated H56. We systematically replaced DDA with either DPPC or DPPG and found that these modifications resulted in colloidally stable liposomes that have similar size and morphology to unmodified CAF01. DPPC- or DPPG-modified CAF01 displayed surface charge-dependent protein adsorption and induced slightly higher follicular helper T cells and germinal center B cells in the lung-draining lymph nodes than unmodified CAF01. In addition, modified CAF01 induced significantly higher levels of H56-specific Th17 cells and polyfunctional CD4⁺ T cells in the lungs, as compared to unmodified CAF01. However, the strong H56-specific humoral responses induced by CAF01 in the lungs and spleen were not influenced by surface charge. Hence, these results provide insights into the importance of surface charge for liposomal adjuvant function and can also guide the design of safe pulmonary subunit vaccines against other mucosal pathogens.

Recombinant Protein Vaccines Formulated with Enantio-Specific Cationic Lipid R-DOTAP Induce Protective Cellular and Antibody-Mediated Immune Responses in Mice

Adjuvants are essential components of subunit vaccines added to enhance immune responses to antigens through immunomodulation. Very few adjuvants have been approved for human use by regulatory agencies due to safety concerns. Current subunit vaccine adjuvants approved for human use are very effective in promoting humoral immune responses but are less effective at promoting T-cell immunity. In this study, we evaluated a novel pure enantio-specific cationic lipid 1,2-dioleoyl-3-trimethylammonium-propane (R-DOTAP) as an immunomodulator for subunit vaccines capable of inducing both humoral- and cellular-mediated immunity. Using recombinant protein antigens derived from SARS-CoV2 spike or novel computationally optimized broadly reactive influenza antigen (COBRA) proteins, we demonstrated that R-DOTAP nanoparticles promoted strong cellular- and antibody-mediated immune responses in both monovalent and bivalent vaccines. R-DOTAP-based vaccines induced antigen-specific and polyfunctional CD8⁺ and CD4⁺ effector T cells and memory T cells, respectively. Antibody responses induced by R-DOTAP showed a balanced Th1/Th2 type immunity, neutralizing activity and protection of mice from challenge with live SARS-CoV2 or influenza viruses. R-DOTAP also facilitated significant dose sparing of the vaccine antigens. These studies demonstrate that R-DOTAP is an excellent immune stimulator for the production of next-generation subunit vaccines containing multiple recombinant proteins.

An inventory of adjuvants used for vaccination in horses: the past, the present and the future

Vaccination is one of the most widely used strategies to protect horses against pathogens. However, available equine vaccines often have limitations, as they do not always provide effective, long-term protection and booster injections are often required. In addition, research efforts are needed to develop effective vaccines against emerging equine pathogens. In this review, we provide an inventory of approved adjuvants for equine vaccines worldwide, and discuss their composition and mode of action when available. A wide range of adjuvants are used in marketed vaccines for horses, the main families being aluminium salts, emulsions, polymers, saponins and ISCOMs. We also present veterinary adjuvants that are already used for vaccination in other species and are currently evaluated in horses to improve equine vaccination and to meet the expected level of protection against pathogens in the equine industry. Finally, we discuss new adjuvants such as liposomes, polylactic acid polymers, inulin, poly-ε-caprolactone nanoparticles and co-polymers that are in development. Our objective is to help professionals in the horse industry understand the composition of marketed equine vaccines in a context of mistrust towards vaccines. Besides, this review provides researchers with a list of adjuvants, either approved or at least evaluated in horses, that could be used either alone or in combination to develop new vaccines.

DnaJ, a promising vaccine candidate against Ureaplasma urealyticum infection

Abstract

Ureaplasma urealyticum (U. urealyticum, Uu) is a common sexually transmitted pathogen that is responsible for diseases such as non-gonococcal urethritis, chorioamnionitis, and neonatal respiratory diseases. The rapid emergence of multidrug-resistant bacteria threatens the effective treatment of Uu infections. Considering this, vaccination could be an efficacious medical intervention to prevent Uu infection and disease. As a highly conserved molecular chaperone, DnaJ is expressed and upregulated by pathogens soon after infection. Here, we assessed the vaccine potential of recombinant Uu-DnaJ in a mouse model and dendritic cells. Results showed that intramuscular administration of DnaJ induced robust humoral- and T helper (Th) 1 cell-mediated immune responses and protected against genital tract infection, inflammation, and the pathologic sequelae after Uu infection. Importantly, the DnaJ protein also induced the maturation of mouse bone marrow–derived dendritic cells (BMDCs), ultimately promoting naïve T cell differentiation toward the Th1 phenotype. In addition, adoptive immunization of DnaJ-pulsed BMDCs elicited antigen-specific Immunoglobulin G2 (IgG2) antibodies as well as a Th1-biased cellular response in mice. These results support DnaJ as a promising vaccine candidate to control Uu infections.

Key points

• A novel recombinant vaccine was constructed against U. urealyticum infection.

• Antigen-specific humoral and cellular immune responses after DnaJ vaccination.

• Dendritic cells are activated by Uu-DnaJ, which results in a Th1-biased immune response.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-12230-4.

Squalene in oil-based adjuvant improves the immunogenicity of SARS-CoV-2 RBD and confirms safety in animal models

COVID-19 pandemic has accelerated the development of vaccines against its etiologic agent, SARS-CoV-2. However, the emergence of new variants of the virus lead to the generation of new alternatives to improve the current sub-unit vaccines in development. In the present report, the immunogenicity of the Spike RBD of SARS-CoV-2 formulated with an oil-in-water emulsion and a water-in-oil emulsion with squalene was evaluated in mice and hamsters. The RBD protein was expressed in insect cells and purified by chromatography until >95% purity. The protein was shown to have the appropriate folding as determined by ELISA and flow cytometry binding assays to its receptor, as well as by its detection by hamster immune anti-S1 sera under non-reducing conditions. In immunization assays, although the cellular immune response elicited by both adjuvants were similar, the formulation based in water-in-oil emulsion and squalene generated an earlier humoral response as determined by ELISA. Similarly, this formulation was able to stimulate neutralizing antibodies in hamsters. The vaccine candidate was shown to be safe, as demonstrated by the histopathological analysis in lungs, liver and kidney. These results have shown the potential of this formulation vaccine to be evaluated in a challenge against SARS-CoV-2 and determine its ability to confer protection.

Nanobionics: From plant empowering to the infectious disease treatment

Infectious diseases (ID) are serious threats against the global health and socio-economic conditions. Vaccination usually plays a key role in disease prevention, however, insufficient efficiency or immunogenicity may be quite challenging. Using the advanced vectors for delivery of vaccines with suitable efficiency, safety, and immune-modulatory activity, and tunable characteristics could be helpful, but there are no systematic reviews confirming the capabilities of the vaccine delivery systems for covering various types of pathogens. Furthermore, high rates of the infections, transmission, and fatal ratio and diversity of the pathogens and infection mechanisms may negatively influence vaccine effectiveness. The absence of highly-effective antibiotics against the resistant strains of bacteria and longevity of antibiotic testing have provoked increasing needs towards the application of more accurate and specific theranostic strategies including the nanotechnology-based ones. Nanobionics which is based on the charge storage and transport in the molecular structures, could be of key value in the molecular diagnostic tests and highly-specific electro-analytical methods or devices. Such devices based on the early disease diagnostics might be of critical significance against various types of diseases. This article highlights the significance of nanobionics against ID.

A comparative study of adjuvants effects on neonatal plasma cell survival niche in bone marrow and persistence of humoral immune responses

The neonatal immune system is distinct from the immune system of older individuals rendering neonates vulnerable to infections and poor responders to vaccination. Adjuvants can be used as tools to enhance immune responses to co-administered antigens. Antibody (Ab) persistence is mediated by long-lived plasma cells that reside in specialized survival niches in the bone marrow, and transient Ab responses in early life have been associated with decreased survival of plasma cells, possibly due to lack of survival factors. Various cells can secrete these factors and which cells are the main producers is still up for debate, especially in early life where this has not been fully addressed. The receptor BCMA and its ligand APRIL have been shown to be important in the maintenance of plasma cells and Abs. Herein, we assessed age-dependent maturation of a broad range of bone marrow accessory cells and their expression of the survival factors APRIL and IL-6. Furthermore, we performed a comparative analysis of the potential of 5 different adjuvants; LT-K63, mmCT, MF59, IC31 and alum, to enhance expression of survival factors and BCMA following immunization of neonatal mice with tetanus toxoid (TT) vaccine. We found that APRIL expression was reduced in the bone marrow of young mice whereas IL-6 expression was higher. Eosinophils, macrophages, megakaryocytes, monocytes and lymphocytes were important secretors of survival factors in early life but undefined cells also constituted a large fraction of secretors. Immunization and adjuvants enhanced APRIL expression but decreased IL-6 expression in bone marrow cells early after immunization. Furthermore, neonatal immunization with adjuvants enhanced the proportion of plasmablasts and plasma cells that expressed BCMA both in spleen and bone marrow. Enhanced BCMA expression correlated with enhanced vaccine-specific humoral responses, even though the effect of alum on BCMA was less pronounced than those of the other adjuvants at later time points. We propose that low APRIL expression in bone marrow as well as low BCMA expression of plasmablasts/plasma cells in early life together cause transient Ab responses and could represent targets to be triggered by vaccine adjuvants to induce persistent humoral immune responses in this age group.